Apparatus for applying dispersions to selected fuel cell electrode plate regions

ABSTRACT

A flowable substance is applied to at least one predetermined area of a major surface of a plate-shaped fuel cell component by directing at least one stream of the flowable substance toward a predetermined zone that is situated in a plane along which the major surface of the component extends, facing the stream. The size of the predetermined zone is smaller than that of the predetermined area, and relative movement along the plane is effected between the component and the predetermined zone so that at least the entire predetermined area of the major surface gradually advances through the predetermined zone in a predetermined advancement direction and path. The stream is controlled so that it is in existence only while the zone is completely within the predetermined area, and until the zone has coincided with all of the predetermined area.

This is a division of copending application Ser. No. 07/813,470 filed onDec. 26, 1991.

TECHNICAL FIELD

The present invention relates to the application of flowable substancesto substrates in general, and more particularly to applying dispersionsto selected regions of fuel cell electrode plates.

BACKGROUND ART

There are already known various constructions of fuel cells, among themsuch in which it is necessary or advantageous to treat selected regionsof various fuel cell components with flowable substances. For example,it may be desired to wetproof such selected regions by applying theretoan initially flowable substance, such as a fluorocarbon dispersion, thatsolidifies after its application and thereafter confers the desiredwetproof characteristic on such regions. The presence of suchfluorocarbon or similar deposits on or in fuel cell electrodes is oftennecessary to create corrosion resistant areas within the cell.

The need for or desirability of providing such wetproofed or similarlytreated regions has already been previously recognized, as has the needfor giving such treated regions quite sharply defined outlines orcontours. Particularly in order to satisfy the last-mentioned need, onemethod that is currently in widespread use for applying such wetproofingor similar compounds is the so-called screen printing process technique,which involves the application of the respective flowable substance,such as a dispersion or "ink", to the selected region or regions of asubstrate through a screen while the remaining regions of the substrateare masked. By properly choosing the consistency or viscosity of thesubstance, the length of the time interval during which the screen/maskmember is in contact with the substrate, the amount and distribution ofthe substance present on the screen/mask member at the beginning of suchtime interval, and the manner in which the substance is forced, such asby a squeegee or the like, through the screen, it is possible tocontrol, within limits, not only the degree of conformity of the contourof the thus treated region to the desired one, but also, when thesubstrate is porous, the depth of penetration of the substance into thesubstrate at the affected region.

However, experience has shown that, while the screen printing process isideally suited for applying thin coats of dispersions on the surfaces ofsmooth surfaced substrates, it in many instances leaves much to bedesired when it is attempted to use it for applying coatings to rough orporous substrate. Moreover, this process is not capable of easily andreliably forcing a semi-liquid substance into the structure of a porousmaterial, particularly when it is desired to cause the substance topermeate into more than just the area immediately underlying the surfaceto which the substance is applied and especially when the substance isto impregnate the selected region of the substrate throughout thethickness of the latter. Yet, such impregnation has been accomplished inthe past with some degree of success by screen printing the part whileit was held under partial vacuum that is applied in such a manner as todraw the substance deeper into the substrate. Nevertheless, even thisprocess is less than satisfactory in many cases, especially because theconstraints placed on the selection of the viscosity of the substance byuse of the screen printing process, in combination with the vagaries ofthe vacuum drawing process, result in less than ideal impregnation ofthe affected region of the substrate by the substance and/or in lessthan accurate definition of the boundary of the affected region orconformity to its desired course. More particularly, given the nature ofvariations in substrate pore spectra and the vagaries of screen processprinting, dimensional control of the fluorocarbon deposit is difficultto achieve. In addition, the necessity for a screen process fluorocarbonink which will penetrate the porous substrate, particularly anelectrode, and yet not run through the screen between printing cyclesmakes the process difficult to manage. Based on the aboveconsiderations, it has been determined that the screen printing processis not suited to high production subsurface wetproof application.

Accordingly, it is a general object of the present invention to avoidthe disadvantages of the prior art.

More particularly, it is an object of the present invention to provide amethod of impregnating selected regions of porous substrates, especiallyof fuel cell electrode plates, with flowable substances capable ofsubsequent solidification, which method does not possess thedisadvantages of the known methods of this kind.

Still another object of the present invention is to develop theimpregnating method of the type here under consideration in such amanner as to assure penetration of the substance into and substantiallyuniform distribution of such substance throughout the affected region ofthe porous substrate.

A further object of the present invention is to present a method of theabove kind the performance of which will result in much bettercoincidence than before of the actual boundaries of the impregnatedregion with the desired ones.

It is yet another object of the present invention to devise an apparatusthat is well suited for the performance of the method of the above type.

A concomitant object of the present invention is design the apparatus ofthe above type in such a manner as to be relatively simple inconstruction, inexpensive to manufacture, easy to use, and yet reliablein operation.

DISCLOSURE OF THE INVENTION

In keeping with these objects and others which will become apparenthereafter, one feature of the present invention resides in anarrangement for applying a flowable substance to at least onepredetermined area of a major surface of a plate-shaped fuel cellcomponent. This arrangement includes means for supporting the componentin such a manner that the major surface thereof extends along apredetermined plane and faces in a given direction, and means fordirecting at least one stream of the flowable substance substantiallyopposite to the given direction toward a predetermined zone that issituated in the aforementioned plane. There is further provided meansfor effecting relative movement between the component supported on thesupporting means and the directing means in such a predeterminedadvancement direction and path along the above plane that at least allof the predetermined area of the major surface is gradually juxtaposedwith the predetermined zone, and means for controlling the directingmeans in such a manner that the stream is in existence only while thepredetermined zone is completely within the predetermined area, anduntil the zone has been juxtaposed with all of the predetermined area.

In accordance with another facet of the present invention, there isprovided a method of applying a flowable substance to at least onepredetermined area of a major surface of a plate-shaped fuel cellcomponent, this method including the steps of supporting the componentin such a manner that the major surface thereof extends along a planeand faces in a given direction, effecting such relative movement alongthe aforementioned plane between the component and a predetermined zonesituated in the plane that at least the entire predetermined area of themajor surface gradually advances through the predetermined zone in apredetermined advancement direction and path, and controlledly directingat least one stream of the flowable substance substantially opposite tothe given direction toward the predetermined zone in such a manner thatthe stream is in existence only while the predetermined zone iscompletely within the predetermined area, and until the zone hascoincided with all of the predetermined area.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be described in more detail below withreference to the sole FIGURE of the accompanying drawing, which is asomewhat simplified, partially sectioned, front elevational view of anapparatus constructed in accordance with the present invention forapplying a dispersion to a selected region of a porous substrate.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawing in detail, and first to FIG. 1 thereof, itmay be seen that the reference numeral 10 has been used therein toidentify a machine or apparatus for applying a flowable substance to aplate-shaped substrate or another, similar, workpiece 20. Moreparticularly, the apparatus 10 has been illustrated, and will bedescribed herein, mainly as being used to perform an improved methodaccording to the present invention for applying a fluorocarbondispersion to specific surface and porous subsurface areas of theworkpiece 20, particularly of a porous fuel cell electrode.

The apparatus 10 includes, as some of its main components, a mainsupport 11, a workpiece support 12 to be used for supporting theworkpiece or substrate 20 in such a manner that a major surface 21 ofthe substrate 10 faces in the upward direction, and an applicator device30 that is mounted on the main support 11 in such a manner as to beimmovable or stationary relative thereto. The workpiece support 12, onthe other hand, is constructed in such a manner as to enable relativemovement between the respective workpiece 20 supported on the workpiecesupport 12 and the applicator device 30 along a plane that includes themajor surface 21 of the substrate 20, at least in an advancementdirection that is substantially normal to the plane of the drawing. So,for instance, the workpiece support 12 may advantageously be constitutedby a belt conveyor of any known construction which not only supports theworkpiece 20 but also advances the same in the aforementionedadvancement direction with respect to the main support 11 and thusrelative to the applicator device 30. This relative advancement movementis diagrammatically indicated in the drawing by the presence of a drive13, and of two connecting lines 14 and 15 which connect the drive 13with the main support 11, on the one hand, and with the workpiecesupport 12, on the other hand, to represent the fact that the drive 13is mechanically connected with the supports 11 and 12 and causesadvancement of the workpiece 20 in the advancement direction withrespect to the applicator device 30. A guide rail 16 is shown to bemounted on the main support 11 in such a position relative to theworkpiece support 12 that the workpiece 20 supported on the latter isguided thereby and hence the transverse position of the workpiece 20 onthe workpiece support 12 is determined with a high degree of precision,especially when a similar and complementary guide rail is arranged atthe other side of the workpiece support 12.

The applicator device 30 is shown to include two applicator assemblies31 and 31' that are similar to one another in so many respects, both asto their structure and their operation, that the same referencenumerals, distinguished from one another merely by the presence orabsence of a prime, have been used to identify them and their respectivecorresponding parts. Moreover, because of this similarity, only theapplicator assembly 31 will be described here in some detail; however,and it is to be understood that, unless indicated otherwise, thisdescription is equivalently applicable to the assembly 31'.

The applicator assembly 31 includes a receptacle 32 that bounds aninternal chamber 33 that is partially filled with a body 34 of aflowable substance that is to be applied by the applicator assembly 31to a selected region 22 of the porous substrate 20. The flowablesubstance body 34 is replenished by feeding additional amounts of theflowable substance into the chamber 35 via a supply conduit 35. For areason that will be presented later, it is desirable for the uppersurface of the flowable material body 34 to rise in the chamber 33 onlyto a predetermined level, and to remain substantially at this level forthe entire time of operation of the applicator device 20. As can beperceived from the drawing, this is achieved in the applicator assembly31 by providing an overflow conduit 36 that opens into the chamber 33 atthe predetermined level and is operative for discharging as much of theflowable substance as would cause the upper surface to rise to ameaningful extent above the predetermined level.

The receptacle 31 is shown to be mounted on a housing 37 which is thatof an on/off valve device 40 that is of a conventional construction andincludes an internal passage that is closable by a valve member and, inthe open position of the valve member, connects the chamber 34 with aninterior of a tubular connecting element 38 which, in turn, communicateswith an internal passage of a tubular applicator element 39 that isshown to have a configuration reminiscent of that of a hypodermicneedle. The valve device 40 is of the type in which the aforementionedvalve member is switched between its open and closed positions inresponse to external signals. It has been found to be advantageous touse a solenoid-operated valve device as the valve device 40. Then, thevalve device 40 further includes a solenoid or actuator housing 41 thatis shown in the drawing as being mounted on the main support 11 andcarrying the valve housing 37 and accommodates a solenoid or a similaractuator that is connected, in a well known manner, with the valvemember such as to displace it, in response to signals received from acontroller 50 via an electrical connecting line 51, between its open andclosed positions.

It will be appreciated that, when the valve member of the valve device40 is in its open position, the flowable substance of the body 34 willflow though the internal passage of the valve housing 37, then throughthe interior of the connecting element 38 and that of the applicatorelement 39 to ultimately leave the latter and be sprayed onto orotherwise directed against the major surface 21 of the workpiece 20 andmore particularly the zone of the major surface 21 that overlies theregion 22 of the workpiece 20.

Now, as may be perceived from the drawing, the only significantstructural difference between the applicator assemblies 31 and 31' isthat the diameter of the tubular applicator element 39 (or, moreimportantly, that of the internal passage thereof) significantly exceedsthe diameter of the tubular applicator element 39' (or that of itsinternal passage). As a result, when the valves 40 and 40' are in theiropen states, the volumetric rate of flow of the flowable substance to beapplied to the region 22 through the applicator element 39 greatlyexceeds that taking place through the applicator element 39', so thatthe applicator assembly 31 supplies a relatively huge amount of theflowable substance to the region 22 but with relatively low precision asfar as the boundary definition is concerned, and can thus be calledcoarse directing means. On the other hand, the applicator assembly 31',while delivering only a minute proportion of the total amount of theflowable substance to the region 22, does it with high precision andhence can be referred to as fine directing means.

It may be seen in the drawing that the applicator element 39' is offsetin a direction normal to the aforementioned advancement directionrelative to the applicator element 39, so that it directs its relativelyfine stream against a boundary zone of the region 22, thus preciselydefining the boundary of the region 22, while the coarse stream issuingfrom the applicator element 39 delivers the bulk of the flowablesubstance to all but the border zone, thus not impairing the precisionof the definition of the affected region 22. It may also be perceivedfrom the drawing that the applicator assemblies 31 and 31', and thus theapplicator elements 39 and 39' are also offset from one another in theadvancement direction, so that the zones against which they direct theirrespective streams at any instant of time are not necessarilycontiguous.

The apparatus 10 as described so far can be used for applying theflowable substance to the porous workpiece 20 when it is desired for theaffected region 22 to extend over the entire length of a marginalportion 23 of the workpiece 20, that is, all the way from the leadingedge to the trailing edge of the workpiece 20 as considered in theadvancement direction. In this case, when it is desired to apply theflowable substance, which will be described below for convenience ascontaining fluorocarbon material without being limited thereto, suchmaterial is first suspended or dispersed in an aqueous or non-aqueousmedium, then the suspension or dispersion is introduced into the chamber33 of the receptacle 32 (and a corresponding chamber of the receptacle32') to form the respective body, such as 34, therein, and finally theflowable substance is dispersed through the applicator elements 39 and39'. The discharge of the fluorocarbon dispersion through each of theapplicator elements 39 or 39' takes place at a substantially constantpressure. This is so because of the provision of the respective overflowtube 36 or 36' which prevents the upper surface of the respectiveflowable substance body, such as 34, to rise above the aforementionedpredetermined level, coupled with the supply of the replenishmentflowable substance through the respective supply pipe or conduit 35 or35' at a rate that is sufficient for the upper surface of the respectiveflowable substance body, such as 34, not to drop more than to anegligible extent below the predetermined level. Because of theresulting maintenance of the respective flowable substance body uppersurface at the predetermined level, the pressure head of such body, suchas 34, remains substantially constant as well throughout the flowablesubstance dispensation process. The volumetric flow rate through theapplicator elements 39 and 39' can be selected, though, either bychanging the vertical location of the overflow tube 36 or 36', or byreplacing the respective applicator element 39 or 39' by another onehaving an internal passage of a different cross-sectional area, or both.It will be appreciated that the volumetric flow rate and the speed atwhich the affected region 22 passes through the respective stream aredeterminative of the amount of the flowable substance that is depositedonto any zone of the major surface 21 of the workpiece 20 at theaffected region 22, and thus the fluorocarbon loading and/or depth ofpenetration of the fluorocarbon substance into the subsurface areas ofthe workpiece 20 and thus the vertical dimension of the affected region22. Thus, while this region 22 has been shown to extend only to a smalldistance below the major surface 21, it is to be undertsood that enoughof the flowable substance could be deposited for the affected region 22to extend through the entire thickness of the workpiece 20.

In the above scenario, the applicator assemblies 31 and 31' can beoperated in such a fashion that the applicator elements 39 and 39' issuetheir respective streams continuously throughout the dispensationoperation, that is, whether or not there is a workpiece 20 in the pathsof such streams at a particular time. However, it is also contemplatedin this situation to use the valves 40 and 40' to intermittently allowand stop the flow of the flowable substance therethrough such that theabove streams will be in existence only from shortly before the leadingedge of the workpiece 20 enters the respective stream path to shortlyafter the trailing edge of the workpiece 20 leaves such path.Alternatively, the streams could be permitted to run constantly, butthey could be diverted during the times that no workpiece 20 is situatedin their paths. In either event, provisions are made for capturing andrecirculating the flowable substance that, for one reason or another,does not reach, or remain on, the respective workpiece 20. It is to benoted that the marginal portion 23 of the workpiece 20 extends in acantilevered manner beyond the workpiece support 12 so that any of theflowable substance that reaches the lower major surface of the workpiece20 underneath the region 22 will not come into contact with theworkpiece support 12.

The workpiece advancement speed, which is kept substantially constant,is so coordinated with the cross-sectional areas of the internalpassages of the applicator elements 39 and 39' and with the pressureheads mentioned above as to achieve the desired loading of fluorocarbonand/or the desired subsurface impregnation depth. A large-size internalpassage and and slow advancement speed give high loadings, andvice-versa. As mentioned before, it was established that applicatorelements, such as 39', having small internal passage diameters yieldbetter dimensional control than those, such as 39, with larger internalpassage diameters. Therefore, it is typically to use both of theapplicator elements 39 and 39' as mentioned before, with the applicatorelement 39 providing for a heavy loading, and with the applicatorelement 39' directing its stream at the affected region perimeter whereimproved dimensional control is desired. Upon deposit, the fluorocarbondispersion quickly and uniformly wicks into the interior of thesubstrate or workpiece 20.

Of course, when it is desired to operate the applicator assemblies 30and 30' in the intermittent fashion that has been discussed above, forinstance to minimize the amount of the flowable substance that has to berecirculated, it is necessary to determine the position of the workpiece20 as it advances on the workpiece support 12 and to supply thisinformation to the controller 50 to enable the latter to activate orinactivate, that is to open or close, the valves 40 or 40' at the propertimes. This determination is even more important when it is desired forthe affected region 22 to commence at a certain distance from theleading edge, or terminate at a certain spacing from the trailing edge,of the workpiece 20, or both.

One approach to making this determination is also illustrated in thesole FIGURE of the drawing, but it is to be understood that the depictedapproach is illustrative only and may be modified in a variety of wayswhile still achieving the same purpose or results. As shown there, adetector device 60 is mounted on the main support 11. The detectordevice 60 includes a roller 61 that is rotatably mounted on a yoke 62 bymeans of two stub shafts 63 and 64. The yoke 62, in turn, is secured toan actuator member 65 which is mounted on the main support 11 formovement in opposite vertical directions and projects into an electricalswitch 66. In use, the elements 61 to 65 are in their non-illustratedlower positions until reached by the leading edge of the workpiece 20 asthe latter advances on or with the workpiece support 12 relative to themain support 11, upon which the further advancement of the workpiece 20causes the lifting of the elements 61 to 65 toward and into theirillustrated raised position, with attendant switching of the electricalswitch 66 from one of its conductive and non-conductive stages andconsequent generation of an electrical signal that is supplied throughan electrical line 67 to the controller 50, apprising the latter of thearrival of the leading edge at a predetermined location. On the otherhand, when the trailing edge of the workpiece 20 advances past suchpredetermined location, the elements 61 to 65 return to their initialpositions and the switch 66 is switched into the other of its states.

The controller 50 is so constructed, in any well-known manner, as to beoperative for issuing into the lines 51 and 51' the valve activatingcontrol signals only after the leading edge of the workpiece 20 hasmoved the desired distance beyond the location at which its arrival hasbeen detected by the detection device 60, and the valve inactivatingcontrol signals only after the workpiece has moved an additionaldistance beyond this position. One way of determining such advancementdistances is to supply to the controller 50, as illustrated through aline 17, a signal indicative of the advancement speed conferred by thedrive 13 on the workpiece 20. In the alternative, or in addition, theangular speed of the stub shaft 64, and thus of the roller 61 which isin rolling contact with the major surface 21 of the workpiece 20 betweenthe time of first contact thereof with the leading edge and the time ofits final contact with the trailing edge of the workpiece 20, isdetected by an angular speed detection device 70, and this informationis supplied through a connecting line 71 to the controller 50 forcalculation of the advancement distance therefrom. Of course, themovement of the elements 61 to 65 toward their lower positions, and theresulting change in the value of the signal appearing on the line 67,could be used for terminating the flowable substance flow instead.

It will be appreciated that the use of the expedients described aboveresults in a more uniform fluorocarbon application than before.Dimensional control is also improved. The approach revealed here is alsomore amenable to continuous high speed production techniques and canreadily be automated to run without operator assistance. While it istrue that the apparatus 10 described above does not have the ability tocreate as complex a pattern as can be created with screen processprinting, a pattern of wetproof and non-wetproof areas can neverthelessbe made by defining the locations of fluorocarbon delivery or applicatorelements 39 and 39' over the workpiece or electrode support or conveyor12. In addition, the respective stream may be interrupted or madediscontinuous by the valve 40 or 40' or by diversion while the workpiece20 is passing under the tubular applicator element 39 or 39' in order tocreate non-wetproof areas.

Typically, it was possible to produce wetproofed areas on porous carbonsubstrate having fluorocarbon loadings of from 0.15 to 0.3 grams percubic centimeter of electrode substrate. The loading was normally heldwithin ±3% of set value with this method. Dimensional control ofwetproofed areas was held to ±0.050". All in all, this method producessubstantially uniform impregnation of fluorocarbon dispersions inaccurately dimensionally defined areas of the electrode or a similarporous workpiece 20.

While the present invention has been illustrated and described asembodied in a particular construction of an apparatus for applyingfluorocarbon dispersions to fuel cell electrodes, it will be appreciatedthat the present invention is not limited to this particular example;rather, the scope of protection of the present invention is to bedetermined solely from the attached claims.

We claim:
 1. An apparatus for applying a flowable substance onto a flatsurface of a plate-shaped fuel cell comprising:a means for supportingthe flat surface, a means for directing a fine stream and a coarsestream of flowable substance onto a predetermined area of the flatsurface, wherein said fine stream applies the flowable substance to atleast a portion of the perimeter of the area of the flat surface, andsaid coarse stream applies additional flowable substance onto theremaining predetermined area of the flat surface, and wherein the finestream applies the flowable substance at a volumetric rate lower thanthe volume rate of the coarse stream, a means for effecting relativemovement between the fine and coarse streams and the flat surface in anadvancement direction to position that area of the flat surface to whichthe flowable substance is to be applied into alignment with the fine andcoarse streams to achieve the desired application, and a means forcontrolling said directing means so that said streams are in existenceonly when the streams are within the predetermined area.
 2. Thearrangement as defined in claim 1, wherein said coarse and finedirecting means include respective conduit members bounding respectivepassages having flow-through cross-sectional areas that are large andsmall relative to one another, respectively, and means for separatelysupplying the flowable substance to each of said passages.
 3. Thearrangement as defined in claim 1, wherein each of said coarse and finedirecting means includes at least one conduit member bounding at leastone passage, and means for supplying the flowable substance to saidpassage; and wherein said controlling means includes an on-off valveinterposed in said supplying means upstream of said passage, means fordetermining the position of the area of said surface to which theflowable substance is to be applied, and issuing a signal representativethereof, and operating means for causing said valve to assume andmaintain, in response to said signal, its open state in which it permitsflow of the liquid substance through only when said area to which theflowable substance is to be applied is in the path of said streams. 4.The arrangement as defined in claim 3, wherein said determining meansincludes means for sensing the position of the component on saidsupporting means relative to said directing means.
 5. The arrangement asdefined in claim 4, wherein said sensing means includes means fordetecting the arrival of a leading edge of the component as consideredin said advancement direction during said relative movement thereof at alocation that is stationary relative to said directing means, and meansfor determining the distance traveled by the component in saidadvancement direction subsequent to such detection; and wherein saidoperating means is operative for initially switching said valve into itsopen position, and for subsequently returning said valve into saidclosed state thereof when said distance determined by said determiningmeans reaches such an ultimate value that said zone is at a terminationspacing ahead of a trailing edge of the component as considered in saidadvancement direction.
 6. The arrangement as defined in claim 3, whereinsaid supplying means includes means for keeping the pressure at whichthe flowable substance is supplied to said passage at a level thatresults in the required volumetric flow rate through said passage. 7.The arrangement as defined in claim 6, wherein said supplying meansincludes a receptacle bounding a chamber disposed above and in opencommunication with said valve for accommodating a body of said flowablesubstance, means for feeding said flowable substance into said chamberin a quantity at least sufficient for an upper surface of said body tobe established at least at such a level that the pressure head of theflowable substance of said body results in said pressure level in saidpassage, and means for discharging from said chamber any excess amountsof said flowable substance that would cause said upper surface to riseabove said level.